Reactor vessel with a mixing device



y 1968 1.. L. VAN DIERENDONCK ETAL 63 REACTOR VESSEL WITH A MIXING DEVICE Filed Dec. 21, 1966 ofmguwsaw United States Patent 3,392,963 REACTOR VESSEL WITH A MIXING DEVICE Laurentius L. van Dierendonck and Willy J. I-iendriks, Geleen, Netherlands, assignors to Stamicarbon N.V., Heerlen, Netherlands Filed Dec. 21, 1966, Ser. No. 603,651 Claims priority, application Netherlands, Dec. 23, 1965, 6516783 7 Claims. (Cl. 259-21) ABSTRACT OF THE DISCLOSURE A mixing vessel having a generally cylindrical jacket and a coaxial guide tube terminating short of the ends of the jacket has shaft mounted, axially spaced propeller stirrers therein rotatable from outside the vessel; feed tubes are provided to introduce fluid components to the vessel adjacent each stirrer, further supply, and discharge components are provided through ports in the vessel end regions. Helical strips, rotatable from the exterior of the vessel are coaxially provided in the annulus between the guide tube and the jacket. Each band has a pitch of at most 0.75 the diameter of the vessel, 2. width of about 0.2 times the diameter of the vessel and a revolution per time multiplied by circulation time equal to, at most, 20. The pumping effect produced by the helical strips decreases mixing time by a factor of seven.

Background of the invention In German Democratic Republic (East German) patent specification 8,794, a mixing device is disclosed in which transport of liquid within a vessel is effected by a propeller mounted in a guide tube within the vessel. However, if highly viscous media were to be mixed in the vessel, and the components to be mixed required a very short retention time in the vessel, the transport capacity of the disclosed propeller would be insufficient, even if the propeller were replaced by a conveyor screw, such as is indicated in Dutch patent application No. 264,617 (laid open for public inspection).

However, to obtain a proper micro-mixing efiect, a propeller or for instance a turbine stirrer, located within the guide tube is particularly suitable. The problem resides in the realization that since rapid equalization of concentration in the entire liquid is needed and a propeller or turbine stirrer provides intimate mixing but only in a small slowly advancing zone, auxiliary means must be provided in order to promote rapid flow of the medium past the stirrer in the guide tube. Previously, it has been proposed to effect rapid circulation of the vessel contents, by means of a circulating pump mounted outside the vessel. Such a solution has the drawbacks that when such a pump is used, the supply and discharge conduits to and from the pump can readily get plugged and undesired piston flows may form in these conduits and because a large pumping capacity is required for highly viscous liquids. In addition, the mean retention time of the medium in the system is significantly raised.

Summary of the invention According to the invention, the transport means consists of one or more helical strips that are freely coaxially rotatable in the annular space between the inner wall of the vessel and the outer wall of the guide tube. A transport means consisting of such a helical ribbon that is freely rotatable between two fixed walls is little sensitive to the viscosity of the medium and its pumping action consequently has a higher efliciency than that of other transport means and/or pumps. If use is made of two helical strips, the dimensions of each strip are ice preferably such that, at a usual pitch of the strips of at most 0.75 times the diameter of the vessel, the strip width is 0.2 times the diameter of the vessel and that revolutions times circulation time equals at most 20, both referred to the same unit time. The flow through the guide tube caused by the helical strip, which acts as a pump, can effect a very rapid equalization of the concentration when use is made of rapidly rotating s'tirrers such as, propellers within the guide tube, while the retention time of the medium in the vessel is very considerably reduced. In many cases components that have to be added cannot be premixed on account of the undesired formation of precipitates and/or undesired loss in activity as a result of the reactions between the components, which are sometimes extremely rapid.

Within the purview of the invention, it is possible to use several spaced propellers and to place the feed means for each of the components to be mixed upstream of a respective stirrer as seen in the direction of flow. Several components can thus be mixed separately with the circulating medium by the stirrers. In polymerization processes, such as the preparation of so-called EPT rubbers, terpolymers, and the like, it is possible using the apparatus of the invention for components that must not be admixed simultaneously to be added to the main flow separately and immediately after each other.

Brief description of the drawing FIGURE 1 is a longitudinal sectional view of a reactor vessel provided with mixing and transport means according to the principles of the invention; and

FIGURE 2 is a transverse cross-sectional view through the vessel of FIGURE 1 approximately at the midpoint thereof, taken substantially along the line II-II of FIG- URE 1.

Description of the preferred embodiment A mixing vessel, which is a reactor vessel in the embodiment shown, is composed of a substantially cylindrical jacket consisting of two opposed cupped sections 1' and 1" which are detachably connected e.g. by means of flanges 2' and 2". Within the vessel there is an annular partition 3 arranged coaxially which is sufliciently short that it does not extend to the end surfaces of the vessel and which forms a guide tube 4. One side of this tube is supported by rigidly connecting it to jacket 1' via axially extending, widely angularly spaced legs which define sufficiently large openings between them to allow a liquid flow to pass without much resistance. The guide tube 4 encloses stirrers 6, 6, 2-blade propeller stirrers. Additional, similarly spaced stirrers could be provided. Consequently, the guide tube actually forms a mixing chamber. The propellers are rigidly connected to a rotatable shaft 7, which extends through a stufling box 8 outside the vessel, where it can be driven. Each propeller gives a particularly good micro-mixing over a short distance of the mixing tube, provided speed and propeller are so chosen that (revolutions per second) multiplied by (diameter in meters) equals at least 0.05 m? per second. The components to be mixed can be passed into the reactor separately in such a way that each component is mixed separately with the parent fiow before a propeller, as seen in the direction of flow. The abovementioned polymerization can be properly effected in this vessel by adding one catalyst component through one feed tube and a second component through another feed tube, and by distributing starting materials, vehicle and the like over these two flows or adding them separately. To this end feed tubes 9, 9' etc. are provided which can feed a component to propeller 6, 6' etc., respectively. The supply and discharge of the parent flow can be effected through ports 10 and 10'. Mounted coaxially in the annular space between the wall of vessel port 1; and the wall of mixing tube 4 are helical strips 11 and 11', which are connected to a fork 12 capable of rotating the strips about the axis of the vessel by means of the rotatable shaft 13 to the end of which fork 12 is rigidly connected. This shaft extends through a stuffing box 14 outside the vessel from where it can be driven. If use is made of two strips, for instance angularly spaced 180 degrees from each other, the dimensions of the strips are preferably such that, at a usual pitch of the strips of at most 0.75 times the diameter of the vessel, the strip width is 0.2 times the diameter of the vessel and that revolutions times circulation time equals at most 20, both referred to the same unit time. From this it follows that the actual size of the vessel is not subject to limitations to obtain the above advantages, provided the above conditions are observed. Because of their pumping action, the helical strips produce a rapid circulation of the liquid through the mixing chamber, as is indicated in the drawing by means of arrows. A combination as shown in the drawing makes it possible to reduce mixing time from, for instance, 35 seconds to seconds.

Example The effectiveness of a combination of transport and stirrer means structured according to the principles of the present invention appears from the example below, where circulation time and mixing time are defined as follows:

Circulation time (T effective content of a vessel in litres elfective pumping capacity of helical strip in litres/second Mixing time (r )=time needed so to equalize the con centration of a substance fed so that the local concentration throughout the body of the mixture difiers less than 5% from the calculated value for the homogeneousness of the mixture.

A solution of methylene blue in water is injected near the propeller into a solution of carboxymethyl cellulose in water (viscosity=100 poises) in a 20-litre vessel provided with a double helical strip and a guide tube with a single propeller therein. Under the conditions indicated, the circulation and mixing times are as follows:

(a) Only the helical strip in operation, making 60 revolutions per second:

=6 seconds, and T =40 seconds The circulation time T is hardly influenced by the propeller and amounts to 5 seconds in the last case.

Naturally, the application need not be limited to open vessels and to mixing, but particularly its use in closed reactor vessels and/or for dissolving components in a circulating medium is conceivable. In a reactor vessel intended for polymerization processes and provided with a device according to the invention, each stirrer preferably has a number of revolutions per second times (diameter in meters) of at least 0.2 m? per second, at a circulation time of the medium in the vessel of at most seconds.

The wall of the guide tube may be made double and a heat-exchanging medium may be circulated between the two elements of the wall. It is furthermore not necessary that the propellers should be driven by one shaft. Several separately driven propellers are within the purview of the invention. In addition, the shafts of the rotating elements may also be driven by means mounted in the vessel, so that these shafts need not extend through the wall of the vessel.

Because the invention described hereinabove, can be considerably modified without departing from the principles of the invention as set forth herein, the invention should be understood as encompassing all such modifications as are within the spirit and scope of the following claims.

What is claimed is:

1. A device for mixing two or more fluid components comprising: a vessel having a generally cylindrical side wall extending between end walls; a guide tube coaxially received within the vessel and spaced from the vessel side wall so as to define an annulus between the interior side wall and the exterior of the guide tube; both ends of the guide tube opening into the vessel so as to be in free communication therewith; at least one rotatable stirring member received within the guide tube and transport means comprising at least one helical strip coaxially received in said annulus for rotation therein with respect to the guide tube and vessel side wall about the longitudinal axis of the vessel.

2. The mixing device of claim 1 wherein the transport means comprises two helical strips spaced substantially degrees apart, and means for rotating the two helical strips conjointly.

3. The mixing device of claim 1 wherein the transport means comprises two like helical strips the pitch of each of which is at most 0.75 times the interior diameter 0f the vessel; wherein each strip width, is about 0.2 times the diameter of the interior of the vessel.

4. The mixing device of claim 1 wherein the stirring means comprises at least one propeller stirrer mounted on a drive shaft and constructed and arranged to be driven at such a rate that the number of revolutions per second multiplied times the square of the propeller stirrer diameter in meters, squared equals at least 0.05 meter squared per second.

5. -A process for mixing at least one viscous medium with at least another component within a mixing region comprising a central cylindrical zone and a surrounding annular zone communicated to the cylindrical zone at the ends thereof, and having two like helical strips in the annular zone, each having a pitch which is at most 0.75 times the outer diameter of the annular zone and a width of about 0.2 times the outer diameter of said annular zone, said process comprising:

(a) introducing the viscous medium and said at least one other component into the mixing region;

(b) rotatably stirring the introduced components within (-ti'he cylindrical zone to produce a viscous mixture; an

(c) rotating said helical strips in said annular zone about the longitudinal axis of said annular zone at a rate wherein the number of revolutions of said helical strips multiplied by the circulation time with respect to the same unit time equals, at most, 20.

6. A process for mixing at least one viscous medium with at least another component Within a mixing region comprising a central cylindrical zone and a surrounding annular zone communicated to the cylindrical zone at the ends thereof, and having at least one propeller stirrer within said central cylindrical zone and at least one helical strip coaxially received in the annular zone for rotation therein about the longitudinal axis of the annular zone, said process comprising:

(a) introducing the viscous medium and said at least one other component into the mixing region;

(b) rotating said at least one helical strip independently of said mixing region to transport said viscous 5 6 medium and said at least another component through (b) rotating said at least one helical strip independsaid region; and ently of said mixing region to transport said viscous (c) rotating said propeller stirrer at a rate wherein medium and said at least another component through the number of revolutions thereof per second multisaid region; and plied by the square of the propeller stirrer diameter 5 (c) rotating said propeller stirrer at a rate wherein in meters squared equals at least 0.05 meter squared the number of revolutions thereof per second multiper second. plied by the square of the propeller stirrer diameter 7. A process for preparation of a polymerization mixin meters squared equals at least 0.2 meter squared ture including mixing at least one viscous medium with per second when the circulation time of the compoat least another component within a mixing region com- 10 nents being mixed is, at most, 10 seconds. prising a central cylindrical zone and a surrounding annular zone communicated to the cylindrical zone at the References Cited ends thereof, and having at least one propeller stirrer UNITED STATES PATENTS within said central cylindrical zone and at least one helical strip coaxially received in the annular zone for rotation 15 612,181 10/1898 spufner therein about the longitudinal axis of the annular zone, 721,974 3/1903 Smlth 259 97 said process comprising; 3,160,397 12/1964 Kelecom 259-97 '(a) introducing the viscous medium and said at least one other component into the mixing region; ROBERT JENKINS Primary Examiner 

